1. Field of the Invention
One embodiment of the present invention relates to a light-emitting device, a lighting device, and a display device which are light energy reuse type and an electronic appliance using the light energy reuse type light-emitting device, lighting device, or display device.
2. Description of the Related Art
In recent years, as display devices, various displays such as a liquid crystal display device including a liquid crystal element, a light-emitting device including a light-emitting element utilizing electroluminescence (EL), and electronic paper using an electrophoretic element has been have been competitively developed.
The light-emitting element utilizing electroluminescence is a planar light source, and therefore is considered applicable to light sources such as backlights of liquid crystal displays, lighting devices, and the like in addition to displays, taking advantage for the feature.
On the other hand, as techniques for colored display devices, colored light-emitting devices, and colored lighting devices, a technique for providing a color filter transmitting light in a specific wavelength band emitted from a light source (including light emission from a light-emitting element) and absorbing light other than light in the specific wavelength band emitted from the light source (e.g., Patent Document 1).
However, when the color filter is used, light other than light in the specific wavelength band is absorbed by the color filter, so that there is a loss of light and light emitted from the light source cannot be used effectively. For this reason, in order to obtain desired luminance sufficiently, a loss of light needs to be compensated by light emission from the light source and the intensity of the light emission from the light source needs to be improved. Improvement of the intensity of the light emission from the light source causes a problem of an increase in power consumption as a result.
As described above, a reduction in power consumption is the common object of the display device, the light-emitting device, and the lighting device. Further, in view of current energy issues, a reduction in power consumption and effective energy use are required.
In order to achieve this object, a technique has been proposed in which a multi-colored dye-sensitized solar cell is formed over a display element (e.g., a liquid crystal element and an EL element) and the multi-colored dye-sensitized solar cell is used as a color filter to convert light energy from the display element into electric power, so that the power consumption is reduced (e.g., Patent Document 2).